Re: [PATCH v3] rcu: ftrace: avoid tracing a few functions executed in stop machine

Steven Rostedt
2022-04-26T15:23:00Z

On Tue, 26 Apr 2022 18:55:11 +0800
Patrick Wang <patrick.wang.shcn@gmail.com> wrote:

> Because of the change of stop machine implementation, there are functions
> being called while waiting currently:
>
> ----------------------------------------------------------------
> Former stop machine wait loop:
> do {
> cpu_relax(); => macro
> ...
> } while (curstate != STOPMACHINE_EXIT);
> -----------------------------------------------------------------
> Current stop machine wait loop:
> do {
> stop_machine_yield(cpumask); => function (notraced)
> ...
> touch_nmi_watchdog(); => function (notraced, inside calls also notraced)
> ...
> rcu_momentary_dyntick_idle(); => function (notraced, inside calls traced)
> } while (curstate != MULTI_STOP_EXIT);
> ------------------------------------------------------------------
>
> These functions (including the calls inside) should be marked notrace to avoid
> their codes being updated when they are being called. The calls inside
> rcu_momentary_dyntick_idle() still remain traced, and will cause crash:
>
> rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
> rcu: 1-...!: (0 ticks this GP) idle=14f/1/0x4000000000000000 softirq=3397/3397 fqs=0
> rcu: 3-...!: (0 ticks this GP) idle=ee9/1/0x4000000000000000 softirq=5168/5168 fqs=0
> (detected by 0, t=8137 jiffies, g=5889, q=2 ncpus=4)
> Task dump for CPU 1:
> task:migration/1 state:R running task stack: 0 pid: 19 ppid: 2 flags:0x00000000
> Stopper: multi_cpu_stop+0x0/0x18c <- stop_machine_cpuslocked+0x128/0x174
> Call Trace:
> Task dump for CPU 3:
> task:migration/3 state:R running task stack: 0 pid: 29 ppid: 2 flags:0x00000000
> Stopper: multi_cpu_stop+0x0/0x18c <- stop_machine_cpuslocked+0x128/0x174
> Call Trace:
> rcu: rcu_preempt kthread timer wakeup didn't happen for 8136 jiffies! g5889 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402
> rcu: Possible timer handling issue on cpu=2 timer-softirq=594
> rcu: rcu_preempt kthread starved for 8137 jiffies! g5889 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 ->cpu=2
> rcu: Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior.
> rcu: RCU grace-period kthread stack dump:
> task:rcu_preempt state:I stack: 0 pid: 14 ppid: 2 flags:0x00000000
> Call Trace:
> schedule+0x56/0xc2
> schedule_timeout+0x82/0x184
> rcu_gp_fqs_loop+0x19a/0x318
> rcu_gp_kthread+0x11a/0x140
> kthread+0xee/0x118
> ret_from_exception+0x0/0x14
> rcu: Stack dump where RCU GP kthread last ran:
> Task dump for CPU 2:
> task:migration/2 state:R running task stack: 0 pid: 24 ppid: 2 flags:0x00000000
> Stopper: multi_cpu_stop+0x0/0x18c <- stop_machine_cpuslocked+0x128/0x174
> Call Trace:
>
> Mark the calls inside rcu_momentary_dyntick_idle():
> rcu_preempt_deferred_qs()
> rcu_preempt_need_deferred_qs()
> rcu_preempt_deferred_qs_irqrestore()
> as notrace to prevent this.
>
> Signed-off-by: Patrick Wang <patrick.wang.shcn@gmail.com>
> ---
> v1->v2:
> - Modify log message.

Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>

-- Steve